Which is why, according to a report last week in The Wall Street Journal, an automaker trade group suggests that they should receive extra fuel-economy credits for building safer cars.

The theory is that as more autonomous-driving features are added to cars, they will be safer and the rate of accidents will fall--reducing congestion, and hence fuel consumption from idling cars caught in traffic.

Driver Assists - lane departure prevention

Features now appearing on increasing numbers of new cars include:

automatic braking to avoid collisions or reduce the severity of impacts

adaptive cruise control that maintains a safe distance from a vehicle ahead

lane-departure warning and correction, which keeps a car from drifting out of its marked lane

When rules for the second round of CAFE standards were released in 2012, regulators said that safety advances should only be assessed only on their ability to reduce injuries and deaths, not their impact on either fuel economy or emissions.

While the paper says the National Highway Traffic Safety Administration (NHTSA) is open to considering the idea, the Environmental Protection Agency (EPA) seems less sympathetic.

Gas pump

With the addition of carbon dioxide, a greenhouse gas, to the list of regulated vehicle emissions, the two groups have had to harmonize their standards for emissions (EPA) and fuel efficiency (NHTSA).

In the past, fuel-economy credits have been given for technologies like Flex-Fuel capability, which allows a vehicle to run on E85 ethanol as well as conventional E10 gasoline.